Cheesemakers skilled in their art are able to vary the cheesemaking parameters to adjust widely the composition, texture and organoleptic properties of natural cheese types long available in different parts of the world. Traditional natural cheese can be categorised as a food gel consisting of a hydrated protein matrix in which fat particles are distributed. In cheese, the protein matrix consists mainly of hydrated casein and its reaction products, completed with minerals consisting chiefly of a variety of calcium phosphate salts. Apart from gross composition (fat, protein, water and salt concentrations), the major variables the cheesemaker can manipulate to give a range of textures are the chemical treatment conditions in the vat, eg rennet concentration, time, temperature, ionic concentration and pH. These variables influence the rate and extent of the expulsion of whey from the curd particles during the syneresis process. During syneresis, minerals are expelled from the curd particles along with the other constituents of whey. One of the major minerals influencing cheese curd texture is calcium1, 2. The calcium content of a variety of traditional cheese types is given by Fox3. 1 Robinson R K & Wilbey R A. Cheesemaking 3rd ed. Chapt. 8, Aspen Publishers, Gaithersburg. 1998.2 Creamer L, Gilles J & Lawrence R C. Effect of pH on the texture of Cheddar and Colby cheese, New Zealand Journal of Dairy Science and Technology, 23, 23–35 (1988).3 Fox P F. Cheese: Chemistry, Physics and Microbiology. Vol. 1. General Aspects, 2nd ed. p. 563. Chapman & Hall, London, 1993.
In non-traditional cheese making, the calcium content of the product can be manipulated by a variety of processes that have been revealed previously. See Moran et al (U.S. Pat. No. 6,183,804) as a recent example, who teaches that the calcium content of MPC can be adjusted (ie lowered) by acidification of the milk prior to ultrafiltration. Also taught is that in addition, if desired, sodium chloride can be added to the milk prior to ultrafiltration in order to lower the calcium content. Using these techniques, there is a practical limit to the proportion of the calcium that can be removed during the ultrafiltration of milk because of factors such as protein precipitation4, retentate viscosity and limits to the extent of diafiltration. Additionally, ultrafiltration flux rates may be hindered5 and contamination of the permeate by the added salt or acid can reduce its value. Typically the practical removal limit using membrane techniques on a commercial plant would be about 20% of the calcium. Throughout the description of the present invention, calcium is used as the reference mineral for comparing divalent cations in the modified process streams and products. It should be noted that levels of other minerals, eg magnesium, will also be modified. 4 See Walstra P. On the stability of casein micelles, Journal of Dairy Science 73, 1965–1979 (1999)5 See Eckner K F & Zattola E A. Modelling flux of skim milk as a function of pH, acidulant and temperature. Journal of Dairy Science. 75, 2952–2958 (1992) and also Ernstrom C A, Sutherland B J & Jameson G W. Cheese base for processing. A high yield product from whole milk by ultrafiltration. Journal of Dairy Science. 63, 228–234 (1980)
Arnaud et al (European patent application EP 16292) teaches that essentially 100% of the calcium can be removed from milk and milk products using treatment with cation exchange resin when charged with monovalent cations.
A further method of removing calcium from casein micelles is to chemically bind it using edible sequestering agents such as phosphate or citrate salts. Such agents are known in the art of converting natural cheese into process cheese, process cheese spreads and such products. Such agents are known as “melting salts”. Calcium chelation, using such agents as EDTA in the modification of the solubility characteristics of MPC, was taught by Blazey et al in WO 01/41578.
Arnaud et al (European patent application EP 16292) discloses that cheese treated by cation exchange can be converted into process cheese spread without the need to use melting salts.
We have discovered that by using cation exchange resin treatment and restricting the extent of calcium removal, that there is a range of intermediate calcium concentrations greater than those used in the processes taught by Moran et al and less than the concentrations taught by Arnaud et al that creates the opportunity to produce a range of novel protein gels, cheese and cheese-like products without the use of coagulating enzymes, eg rennet, melting salts or gums.
It is an object of this invention to achieve this desideratum or at least to offer the public a useful choice.
In the only example given in the EP 16292 specification, there is nearly complete calcium removal from the “dairy product” precursor, Cheddar cheese, before the dairy product (process cheese) was prepared. There is no indication or suggestion that the inventors made any attempt to limit the calcium removal to a predetermined level. There is no suggestion that by controlling the level of calcium ions removed, it is possible to produce MPCs suitable for use in making food gels or cheese like gel products with predetermined properties.